Telescopically expanding training cartridges are known. Examples are disclosed by U.S. Pat. No. 5,359,937, WO00/09965 and U.S. Pat. No. 6,564,719 and these disclosures are discussed below.
The cartridge disclosed by U.S. Pat. No. 5,359,937 allows a free flow of gas generated in the cartridge to reach and then propel a bullet through the barrel of a host gun at the same time as the cartridge telescopically expands. The disclosed design has many disadvantages including:
1. Expansion of the cartridge in the gun while the bullet is in the barrel of the gun causes movement of the gun and a loss of accuracy.
2. The velocity of the bullet fired from the gun is dependent on the force required to be generated by the cartridge to open the gun. In this regard, if there is a delay in cycling the gun, this leads to a delay in propelling the bullet and hence there is a velocity variation.3. During the time that there is a free flow of gas to the bullet, an excessive amount of gas is required to expand the cartridge.
The design of cartridge disclosed in WO00/09965 addresses a number of the disadvantages discussed above, namely:
1. The free flow of gas to the bullet is cut off as the cartridge expands to cycle the gun. In light of this, the cartridge disclosed in this document requires less gas compared to the cartridge disclosed by U.S. Pat. No. 5,359,937.
2. The bullet has exited or substantially exited the gun before the cartridge expands to cycle the gun i.e. less movement of the gun, which leads to better accuracy.
However, the velocity of the bullet is controlled by the expansion of the cartridge which in turn is controlled by the force required to cycle the gun. This results in variations in velocity from one gun compared to another gun and from guns produced by one manufacturer compared to those produced by another manufacturer.
The disclosed cartridge design is also very expensive to manufacture.
The design of cartridge disclosed in U.S. Pat. No. 6,564,719 overcomes a number of the disadvantages discussed above, but this cartridge requires two gas generating sources. In this regard, a first rear gas generator is activated by the firing pin of a gun and it fires a second bullet propelling gas generator. The first gas generator cycles the gun after it has fired the second gas generator and the bullet has left the barrel of the host gun.
Cartridges according to this known design are expensive to manufacture and they suffer from the disadvantage that there are inherent variations in bullet velocity caused by the inability to accurately control the volume of gas generated by the bullet propelling gas generator.
The present invention addresses the problems and disadvantages of the known cartridges.
Remarkably, a cartridge according to the invention has been found to have the advantages of improved shot to shot and gun type to gun type bullet velocity. In addition, the internal working components of a cartridge according to the invention control the velocity of a bullet. Advantageously, the velocity of the bullet is not dependent on the gun.
It will be apparent that accurate control of the velocity of a bullet reduces the risk of injury and improves safety.
In addition, the invention provides the advantage that, only one gas generator is required. This reduces manufacturing cost and pollution compared to known cartridges.